Corrosion resistant metal made thermal type mass flow rate sensor and a fluid supply device using the same

ABSTRACT

A corrosion resistant thermal type mass flow rate sensor, and a fluid supply device employing the sensor are provided thus allowing enhanced corrosion resistance of the thermal type mass flow rate sensor, improve responsiveness, to be achieved particle-free, and to prevent unevenness of product qualities. A thermal type mass flow rate sensor is constituted with a sensor part  1  comprising a corrosion resistant metal substrate  2  formed as a thin plate by applying electrolytic etching on the rear face side of a corrosion resistant metal material W, a thin film F forming a temperature sensor  3  and a heater  4  mounted on the rear face side of the corrosion resistant metal substrate  2 , and a sensor base  13  hermetically fitted by welding to the outer periphery of the corrosion resistant metal substrate  2  of the afore-mentioned sensor part  1  fitted into a fixture groove  13   a.

FIELD OF THE INVENTION

This is a National Phase Application in the United States ofInternational Patent application No. PCT/JP2004/001519 filed Feb. 12,2004, which claims priority on Japanese Patent Application No.2003-112090, filed Apr. 16, 2003. The entire disclosures of the abovepatent applications are hereby incorporated by reference.

The present invention is employed mainly to detect a mass flow rate in agas supply line and the like with semiconductor manufacturingfacilities, and is concerned with a corrosion resistant metal madethermal type mass flow rate sensor and a fluid supply device for whichthe sensor is employed, of which all the gas contacting faces are formedof corrosion resistant metals such as stainless steel (SUS316L) and thelike having excellent corrosion resistance even to highly corrosivefluids, enabling to achieve to make it particle-free and leak-free.

BACKGROUND OF THE INVENTION

Conventionally, a capillary thermal type mass flow rate sensor or asilicon-made ultra-small-sized thermal type mass flow rate sensor bymaking use of micro-machine technologies has been widely used to measurea mass flow rate of a liquid in the technical fields such as chemicalanalysis equipment and the like.

The former, or a capillary thermal type mass flow rate sensor ischaracterized by that the sensor allows its gas contacting faces to bemade of stainless steel due to the structure, thus enabling to enhancethe corrosion resistance to fluids to be measured at ease.

However, the capillary thermal type mass flow rate sensor is required tobe equipped with a resistance wire for a heater to be wound to heat acapillary tube, thus causing a problem that may lead to unevenness inproperty among the products.

Another problem may be that the response speed of a mass flow ratesensor becomes slow due to the relatively large heat capacities of thecapillary tube and the resistance wire for a heater.

On the other hand, along with the development in so-called micro-machinetechnologies in recent years, the development and utilization of thelatter, or a silicon-made ultra-small-sized thermal type mass flow ratesensor has been widely under way. It has now become popular not only inthe chemical-related fields but also in the industrial fields such as anautomobile industry and the like due to the reason that a silicon-madeultra-small-sized thermal type mass flow rate sensor can be manufacturedunder a single processing, thus reducing the unevenness in propertyamong the products, and achieving the extremely fast response speed as asensor by making heat capacities small by downsizing, all of which areregarded as excellent characteristics of the sensor.

However, it is noted that there exist many problems to be solved withthe said silicon-made ultra-small-sized thermal type mass flow ratesensor. Among other things, corrosion resistance is one that is neededto be solved urgently. That is, a silicon-made ultra-small-sized massflow rate sensor employs silicon to form gas contacting faces.Therefore, a fundamental difficulty is that it can be easily corroded byfluids in a halogen family and the like.

Furthermore, organic materials such as an epoxy resin, an O-ring and thelike are used as sealing materials for the mass flow rate sensor, thusmaking the emission of particles and the occurrence of the outside leakunavoidable. Accordingly, it becomes unable that the sensor is appliedfor the gas supply line and the like in semiconductor manufacturingfacilities.

At the same time, various technologies have been developed so far tosolve difficulties the afore-mentioned silicon-made ultra-small-sizedthermal type mass flow rate sensor faces.

For example, with the TOKU-KAI No.2001-141540, the TOKU-KAINo.2001-141541, there is provided a heat resistance layer E₆ on theoutermost layer of a film E formed on the upper face of the frame D madefrom a silicon substrate A as shown in FIG. 18. With FIG. 18, E₁˜E₃designate silicon oxide layers to form a film E, E₄ a silicon nitridelayer, E₅ platinum, and C a lead connecting hardware.

[Patent Literature 1]

TOKU-KAI No. 2001-141540 Public Bulletin

[Patent Literature 2]

TOKU-KAI No. 2001-141541 Public Bulletin

OBJECT OF THE INVENTION

With the silicon-made ultra-small-sized mass flow rate sensorillustrated in the afore-mentioned FIG. 18, a silicon nitride E₄ layerformed on the lower face side of a frame D and a heat resistance layerE₆ comprising a silicon nitride layer to form a film E have beenprovided to enhance water resistance and moisture resistance. However,it is far from the fundamental solution for the problems such as theafore-mentioned corrosion and the like due to the reason that the frameD itself is formed with a silicon substrate A.

The present invention is to solve the afore-mentioned problems with theconventional mass flow rate sensor such as {circle around (1)} thatunevenness in property among products might be caused and the responsespeed is low with a capillary thermal type mass flow rate sensor, and{circle around (2)} that the emission of particles, the occurrence ofoutside leaks and the like cannot be avoided with a silicon-madeultra-small-sized thermal type mass flow rate sensor in addition that itis less corrosion resistant. It is a primary object of the presentinvention to provide a corrosion resistant metal made thermal type massflow rate sensor and a fluid supply device for which the sensor isemployed, thus allowing to manufacture ultra-small-sized and consistentproducts by making use of micro-machine technologies, to achieve theexcellent corrosion resistance and the fast response speed, and also toenable to make it particle-free and outside leak-less.

DISCLOSURE OF THE INVENTION

Inventors of the present invention have come to an idea, by employingmicro-machine technologies, to prevent unevenness in quality among massflow rate sensors manufactured, to enhance corrosion resistance andresponsiveness, and further to achieve to make it particle-free andoutside leak-less by forming two pieces of temperature detectingresistance, a heater, a lead wire to connect elements and the likerequired for a mass flow rate sensor by using a thin film body on thesubstrate made of the corrosion resistant metal such as stainless steeland the like; and manufactured trial mass flow rate sensors, and thetests were repeated on them based on the said idea.

The present invention has been created based on the afore-mentioned ideaand the results on various tests. The present invention, in accordancewith a first embodiment, is fundamentally so constituted that it isequipped with a sensor part 1 comprising a corrosion resistant metalsubstrate 2 and a thin film F forming a temperature sensor 3 and aheater 4 mounted on the rear face side of the fluid contacting surfaceof the said corrosion resistant metal substrate 2.

The present invention in accordance with a second embodiment, which is amodification of the first embodiment, is so made that a sensor base 13equipped with a sensor part 1, a fluid inlet to make fluids flow in, afluid outlet to make fluids flow out, and a body 21 equipped with afluid passage for communication between the fluid inlet and a fluidoutlet are connected, and a strain applied to the said sensor part 1when fastening a metal gasket 27 is suppressed by relatively raisingstiffness of the material immediately thereupon against the said metalgasket 27 to secure hermeticity.

The present invention in accordance with a third embodiment, which is amodification of the first embodiment or the second embodiment, is somade that a corrosion resistant metal substrate 2 is formed withthickness of less than 150 μm.

The present invention in accordance with a fourth embodiment, which is amodification of the first embodiment or the second embodiment, is somade that a sensor base 13 equipped with a sensor part 1 installed tosecure hermeticity and a corrosion resistant metal substrate 2 arefastened hermetically by welding.

The present invention in accordance with a fifth embodiment, which is amodification of the first embodiment, the second embodiment, the thirdembodiment or the fourth embodiment, is so made that a thin film F isconstituted with an insulation film 5 formed on the rear face of thefluid contacting face of the corrosion resistant metal substrate 2, ametal film M to form a temperature sensor 3 and a heater 4 formedthereupon, a protection film 6 to cover the insulation film 5 and themetal film M.

The present invention in accordance with a sixth embodiment is so madethat a corrosion resistant metal made thermal type mass flow rate sensorof one or more of the first embodiment, the second embodiment, the thirdembodiment, the fourth embodiment and the fifth embodiment, inclusive,is mounted on a fluid controller, to check the flow rate appropriatelywhen fluids are controlled.

In accordance with the present invention, a mass flow rate sensor ismanufactured by applying micro-machine technologies as in the case ofthe conventional silicon-made ultra-small-sized mass flow rate sensor,thus enabling to reduce the unevenness in quality among the products toa minimum. In addition, the corrosion resistant metal substrate used fora sensor substrate (for example, the SUS316L-made substrate) isprocessed to make it a thin plate with thickness of 30˜80 μm byelectrolytic etching, and a resistance wire and the like are made to bethin films, to make the heat capacity of the sensor part extremelysmall, thus increasing the response speed of the sensor remarkably.

Furthermore, all the gas contacting faces are constituted of a corrosionresistant metal, and a sensor part and a sensor base are assembled bywelding, and a metal gasket sealing is employed to mount a valve bodyand the like, thus enabling to achieve to make it corrosion-free,particle-free and outside-leak-free.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan schematic view of the sensor part of a corrosionresistant metal made thermal type mass flow rate sensor according to thepresent invention.

FIG. 2 is a cross-sectional schematic view taken line A-A of FIG. 1.

FIG. 3 is an explanatory drawing of the operating principle of acorrosion resistant metal made thermal type mass flow rate sensoraccording to the present invention.

FIG. 4 is explanatory drawings of the manufacturing process of a sensorpart, where (a) is a preparation process of the SUS316L wafer, (b) is aformation process of an insulation film 5, (c) is a formation process ofa Cr/Pt/Cr film (a metal film M), (d) is a formation process of aprotection film 6, (e) is a formation process of an electrode insertionhole 7, (f) is an etching process on the rear side of the SUS316L wafer,and (g) is a separation etching process on the sensor part.

FIG. 5 is a sectional schematic view to illustrate an example of acorrosion resistant metal made thermal type mass flow rate sensor.

FIG. 6 illustrates a photo-mask pattern to be used for manufacturing asensor part, and shows a state of a pre-mask pattern being overlaid.

FIG. 7 illustrates a photo-mask pattern to be used for manufacturing asensor part, and shows what is used for the process in FIG. 4( c).

FIG. 8 illustrates a photo-mask pattern to be used for manufacturing asensor part, and shows what is used for the process in FIG. 4( e).

FIG. 9 illustrates a photo-mask pattern to be used for manufacturing asensor part, and shows what is used for the process in FIG. 4( f).

FIG. 10 illustrates the surface coarseness in the event thatelectrolytic etching is performed to the SUS316L-made substrate.

FIG. 11 is a partially enlarged view of an electrolytic etching part Qin FIG. 7.

FIG. 12 is a signal detection circuit diagram of a mass flow rate sensoraccording to the present invention.

FIG. 13 is a diagram to illustrate various characteristics of a sensorpart according to the present invention, where (a) shows therelationship between the heat temperature and the resistance value ofthe temperature detecting resistance, (b) shows the relationship betweenthe heat current and the resistance value of the temperature detectingresistance, and (c) shows the relationship between the gas flow rate andthe sensor output.

FIG. 14 is a diagram to illustrate an example of the flow rate responsecharacteristics of a mass flow rate sensor according to the presentinvention.

FIG. 15 is a sectional view to illustrate an example of the assemblydrawing of a mass flow rate sensor according to the present invention.

FIG. 16 is a sectional view to illustrate the other example of theassembly drawing of a mass flow rate sensor according to the presentinvention.

FIG. 17 is a sectional view to illustrate another example of theassembly drawing of a mass flow rate sensor according to the presentinvention.

FIG. 18 is a sectional view to illustrate an outline of the conventionalsilicon-made ultra-small-sized thermal type mass flow rate sensor.

LIST OF REFERENCE CHARACTERS AND NUMERALS

-   -   S a corrosion resistant metal made mass flow rate sensor    -   F a thin film    -   M a metal film    -   W a corrosion resistant metal material    -   G a gas to be measured    -   1 a sensor part    -   2 a corrosion resistant metal substrate    -   3 a temperature sensor    -   3 a, 3 b temperature detecting resistances    -   4 a heater    -   5 an insulation film    -   6 a protection film    -   7 an electrode insertion hole    -   8 a combined photo-mask pattern    -   9 a photo-mask pattern to form a temperature detecting        resistance and a heater    -   10 a photo-mask pattern to form a lead hole    -   11 a photo-mask pattern (a resist pattern) for etching the rear        face side    -   11 a a groove part    -   11 b a thin substrate part    -   12 a, 12 b negative resists    -   13 a sensor base    -   13 b a fixture groove    -   14 a heater driving circuit    -   15 an offset adjustment circuit (for the coarse adjustment)    -   16 an offset adjustment circuit (for the fine adjustment)    -   17 a gain adjustment circuit for the temperature detecting        resistance    -   18 a differential amplifying circuit    -   19 an output terminal    -   20 a joint part    -   21 a body    -   22 a sensor base presser    -   23 a wiring substrate presser    -   24 a wiring substrate    -   25,26 guide pins    -   27 a metal gasket    -   28 a rubber sheet    -   29 a lead pin    -   30 a lead wire (a gold wire)    -   31 a body    -   32 a pressure detector    -   33 a control valve    -   34 a piezo-electric valve driving device    -   35 an orifice    -   36 a filter

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment in accordance with the present invention is describedhereunder with reference to the drawings.

FIG. 1 is a plan schematic view of the sensor part 1 which is anessential part of a corrosion resistant metal made thermal type massflow rate sensor according to the present invention. FIG. 2 is across-sectional schematic view taken on line A-A of FIG. 1.

The sensor part 1 comprises a thin heat resistant metal substrate 2, aninsulation film 5 formed on the upper face of the substrate 2, atemperature sensor 3 and a heater 4 formed on the upper face of theinsulation film 5, and a protection film 6 formed on the upper faces ofthe temperature sensor 3, a heater and the like. That is, the sensorpart 1 includes outer peripheral part 1 a, which forms the sensor part 1of the corrosion resistant metal material W with thickness of 120˜180 μm(or a heat resistant metal substrate 2), and central part 1 b, which ismade to be a thin plate with thickness of approximately 30˜80 μm, asdescribed later, by removing a part of the rear face side of thematerial W by the method of an electrolytic etching processing (See FIG.5).

A thin film F is formed on the upper face side of the heat resistantmetal substrate 2 with an insulation film 5, a metal film M which formsa temperature sensor 3, a heater 4, and an electric conductive lead part(not illustrated), and a protection film 6.

Furthermore, an electrode insertion hole 7 with an appropriate size isformed on the afore-mentioned protection film by the etching processing.

Thus, a gas G to be measured flows in the direction of the arrow alongthe corrosion resistant metal substrate 2 on the rear face side of thesensor part 1. When this happens, some of the heat quantity the gas Gpossesses move to the corrosion resistant metal substrate 2, thusresulting in that the temperature distribution Tt of the heat resistantmetal substrate 2 shifts from the temperature distribution To wherethere is no flow of the gas G to the temperature distribution Tt asshown in FIG. 3.

As seen above, changes in the temperature distribution of a corrosionresistant metal substrate 2 caused by the flow of the gas G arepresented as changes in the voltage values at the both ends of thetemperature detecting resistances 3 a, 3 b through the mediation ofchanges in the resistance values of the temperature detectingresistances 31, 3 b which form a temperature sensor 3. Thus, a mass flowrate of the gas G can be known by detecting the changes in the voltagevalues as a differential output.

The above stated operating principle of a thermal type mass flow ratesensor is identical with that of a publicly known silicon-made thermaltype mass flow rate sensor. Therefore, the explanation in detail isomitted here.

Referring to FIG. 1 and FIG. 2, a less-than-approximately-150 μm thickthin-plate-shaped metal plate having corrosion resistance is most suitedfor a corrosion resistant metal material W which forms theafore-mentioned sensor part 1. With the embodiment, a stainless steelplate (SUS316L) with thickness off 150 μm is used.

The part which forms a sensor part 1 of the said corrosion resistantmetal material W, that is, a corrosion resistant metal substrate 2(encircled by a dotted line) is made to be thinner by an etchingprocessing as explained later, thus substantially making itapproximately 30˜60 μm thick.

As described later, the afore-mentioned insulation film 5 is an oxidizedfilm with thickness of 1.2 μm˜1.8 μm formed by the so-called CVD method.With the embodiment, a 1.5 μm thick SiO₂ film formed by the CVD(chemical Vapor Deposition) method is used for the insulation film 5.

The afore-mentioned temperature detecting resistance 3 and heater 4 aremade from a metal film M formed by using the mask pattern for the flowrate sensor (not illustrated) on the afore-mentioned insulation film 5.With the embodiment, a temperature detecting resistance 3, a heater 4and the like are made from a metal film M formed by a Cr/Pt/Cr film(with thickness of 10/100/10 μm respectively) being laminated in orderby the vapor deposition method.

The afore-mentioned protection film 6 is a film body covering the upperpart of a temperature detecting resistance 3, a heater 4 and the like.With the embodiment, the 0.4˜0.71 μm thick SiO₂ film formed by the CVDmethod is used.

The said protection film 6 is provided with an electrode insertion hole7 suitably shaped by the plasma etching method, to draw out an electroderod and the like through the said electrode insertion hole 7.

The rear face side of a corrosion resistant metal substrate 2 whichforms a sensor part 1 is finished with thickness of 30˜80 μm by applyingan electrolytic etching to the corrosion resistant metal material W asdescribed later.

A sensor part 1 is eventually separated from a corrosion resistant metalmaterial W by the method of a so-called through-etching processing. Asdescribed later, the separated sensor part 1 is hermetically fixed to acorrosion resistant metal made flow rate sensor base 13 by the laserwelding or the like, to constitute a corrosion resistant metal madethermal type mass flow rate sensor S according to the present invention.

Next, the manufacturing and working process of the afore-mentionedsensor part 1 is described.

FIG. 4 is an explanatory drawing of the manufacturing process of asensor part 1 according to the present invention.

First, a stainless steel made thin plat (SUS316L) with appropriatedimensions, for example, of the diameter of 70 mm φ˜150 mm φ, thethickness of 130˜180 μm is prepared for a corrosion resistant metalmaterial W (FIG. 4( a)). There is no need to say that a thin metal plate(for example, an austenitic steel plate made of a Cr—Ni alloy) otherthan the thin stainless steel plate can be employed for the corrosionresistant metal material W.

Then, a SiO₂ film (an insulation film) 5 with thickness of approximately1.51 μm is formed on the outer rear face of the afore-mentionedstainless steel made thin plate (hereinafter called a SUS316L wafer) byemploying a plasma CVD device (the Plasma-Enhanced Chemical VaporDeposition Device) for which TEOS (Tetra-Ethoxy-Silaue) is used (FIG. 4(b)).

And, there are formed patterns of temperature detecting resistances 3 a,3 b, a heater 4 and the like made from a metal film M formed by aCr/Pt/Cr film (with thickness of 10/100/10 μm respectively) by employingan electronic beam heating type vapor deposition device and photo-maskpatterns 9 illustrated in FIG. 7 on the afore-mentioned SiO₂ film (FIG.4( c)). FIG. 6 illustrates a photo-mask pattern 8 in a state of aphoto-mask pattern 9 being combined with a photo-mask pattern 10 to forman electrode insertion hole 7 as described later.

Then, a SiO₂ film (a protection film) 6 with thickness of approximately0.5 μm is formed on the temperature detecting resistances 3 a, 3 b andthe heater 4 which form a temperature sensor 3 formed in the process ofthe afore-mentioned FIG. 4( c) by employing a plasma CVD for which theafore-mentioned TESO is used (FIG. 4( d)).

After that, there is made a hole with a bore of 200 μm (an electrodeinsertion hole 7) to draw out an electrode on the afore-mentionedprotection film 6 for a temperature detecting resistance 3 and a heater4 by employing a photo-mask pattern 10 to form an electrode insertionhole illustrated in FIG. 8 with a plasma etching device for which CF₄gas is used (FIG. 4( e)).

Due to the reason that the SUS316L material and Cr have a high toleranceto plasma by the CF₄ gas, the etching in progress stops automaticallyupon completion of the etching of a SiO₂ film 6. Therefore, there is norisk for a so-called over-etching.

Upon completion of the afore-mentioned processes on the top face of acorrosion resistant metal material W (the SUS316L wafer), a resistpattern is formed on the rear face side using a photo-mask pattern 11illustrated in FIG. 9, and an etching processing is performed on therear face side of the material W to make the thickness becomeapproximately 50 μm by an electrolytic etching (FIG. 4( f)).

A part 11 a shown in FIG. 4( f) is a groove part to separate the sensorpart 1 from the material W. 11 b is a thin substrate part made thin bythe etching processing.

Lastly, a negative resist 12 a (a spin coat method) and a negativeresist 12 b (a dip coat method) are coated on the rear face side of thecorrosion resistant metal substrate 2 whereon the afore-mentioned filmswere formed and the thin substrate part 11 b on the rear face side. Andthen, the thin substrate part 11 b (with thickness of approximately 50μm) of the groove part 11 a is penetrated circularly by applying anetching treatment with ferric chloride solution (FeCl₃—40wt %) so thatthe sensor part 1 is separated from the material W.

After removing the resists 12 a and 12 b, the circle-shaped sensor part1 separated from the material W is fitted flush into the flat fittinggroove 13 aof the sensor base 13 formed in the shape shown in FIG. 5,and fixed hermetically to the sensor base 13 by laser welding on theouter peripheral part 1 a, thus a corrosion resistant metal made thermaltype mass flow rate sensor S according to the present invention beingconstituted.

With the etching processes shown in the afore-mentioned FIG. 4( f), amixed solution of the sulfuric acid and methyl alcohol is used for theelectrolytic solution, and a photo resist is used for the mask materialto etch the specified parts on the rear face side of the material W.

The coarseness of the rear face after an electrolytic etching wasperformed on the afore-mentioned SUS316L-made substrate 2 is found to beless than Ra 0.1 μm as shown in FIG. 10. This indicates that thereexists no local over-etching.

Namely, it is found that an electrolytic etching method is an extremelyeffective one to conduct etching on the SUS316L due to the reason that agas contacting part in the gas piping system for the semiconductorprocess is needed to be particle-free and corrosion-free.

A part Q in FIG. 10 shows the afore-mentioned electrolytic etching part,and FIG. 11 is an enlarged view of the electrolytic etching part Q.

FIG. 12 shows a signal detection circuit diagram of a mass flow ratesensor according to the present invention shown in the afore-mentionedFIG. 5. The said signal detection circuit comprises a sensor part 1, aheater driving circuit 14, an offset adjusting circuit (for a coarseadjustment) 15, an offset adjusting circuit (for a fine adjustment) 16,a gain adjusting circuit for a temperature detecting resistance 17, adifferential amplifying circuit 18 and the like. With FIG. 12, 3 a and 3b are temperature detecting resistances, and 19 is an output terminal.

Referring to FIG. 12, a sensor part 1 is heated when a heater drivingcircuit 14 starts operating. Resistance values change with thetemperature changes of the upstream side temperature detectingresistance 3 a and the downstream side temperature detecting resistance3 b which form the temperature sensor 3 of the sensor part 1 when thegas G to be measured flows through. The changes are inputted as thechanges in the output voltage to the differential amplifying circuit 18through the gain adjusting circuit 17. The output difference between thetwo values is outputted to the output terminal 19 by way of an operationamplifier 0707.

A corrosion resistant metal substrate 2 which forms the sensor part 1according to the present invention is made to be a thin film byelectrolytic etching. Therefore, there is a possibility that the sensorpart 1 is distorted by the gas pressure when the gas G flows, thusresulting in that the resistance values of the temperature detectingresistances 3 a, 3 b of the temperature sensor 3 might change.

For this reason, in the event that an usual resistant bridge circuit isemployed, there is caused a problem that the output of a sensor part 1changes with the occurrence of distortion. However, with a signaldetecting circuit according to the present invention, it is soconstituted that the rates of amplification of the voltage valuesoutputted from the upstream side temperature detecting resistance 3 aand the downstream side temperature detecting resistance 3 b areindependently adjusted by the offset adjusting circuit 15, and the inputvalues to the differential amplifying circuit 18 are furtherfine-adjusted by the offset adjusting circuit 16. Therefore, the changesin the output voltage values of the temperature detecting resistances 3a, 3 b caused by application of the gas pressure are cancelled by theadjustment of the amplification rates.

As the result, the output changes of the sensor part 1 caused by the gaspressure can be completely suppressed, thus allowing the detection ofthe mass flow rate with the high degree of accuracy.

FIG. 13 is a diagram to illustrate the characteristics of a mass flowrate sensor S according to the present invention. FIG. 13( a) shows therelationship between the temperatures of a heater 4 and the resistancevalues. FIG. 13( b) shows the relationship between the current values ofa heater 1 and the resistance values, and FIG. 13( c) shows therelationship between the gas flow rate (SCCM) and the detection outputvalues (v).

The resistance value of the heater 4 of a sensor part 1 used for themeasurement of various characteristics in FIG. 13 was approximately 2.4kΩ and the resistance values of the temperature detecting resistances 3a, 3 b were 2.0 kΩ (both carrying the same values). The heater 4 was fedwith a current of 10 mA, and the temperature detecting resistances 3 a,3 b were fed with a current of 1.2 mA.

When a gas flow rate was made to change in the range of 0˜100 SCCM, thechanges in the output value of the sensor part 1 was approximately 1.0V(note: the output value was amplified by 500 times by the OP amplifier).

Furthermore, the output value of the sensor part 1 depends on theinterstice (a flow passage height) between the sensor base 13 of a massflow rate sensor S and the fluid passage as shown in FIG. 15 to bedescribed later. Therefore, the possible measuring range of the flowrate can be appropriately changed by adjusting the afore-mentioned flowrate height.

FIG. 14 illustrate an example of the flow rate characteristics of themass flow rate sensor S according to the present invention, and alsoillustrates the characteristics in the event that a gas flow rate is setat 0˜100 SCCM. With FIG. 14, the curve SA illustrates the flow rateresponse characteristics of the mass flow rate sensor S according to thepresent invention, and a graduation on the lateral axis indicates 500msec.

The curve SF illustrates the flow rate response characteristics of themass flow rate sensor with the conventional pressure type flow ratecontrol device under the same conditions.

FIG. 15 illustrates an example of the fluid supplying device equippedwith a mass flow rate sensor S according to the present invention, andalso illustrates a state o the mass flow rate sensor S being fixed tothe joint part 20 mounted on the gas passage. With FIG. 15, 21designates a body of the joint part 20, 22 a sensor base presser, 23 awiring substrate presser, 24 a wiring substrate, 25 a guide pin, 26 aguide pin, 27 a metal gasket, 28 a rubber sheet, 29 a lead pin, and 30 alead wire (a gold wire).

The afore-mentioned guide pins 26,27 are used for the positioning at thetime when a mass flow rate sensor S is fitted into a body 21. The spacebetween the sensor base 13 and the body 21 is hermetically secured bythe metal gasket 27.

The mass flow rate of the gas G flowed in through a fluid inlet 21 a isdetected by the sensor part 1 while the gas G is passing through theinside of the flow passage 21 b, and the gas G flows out through thefluid outlet 21 c toward the outside.

With the present invention, a gas G to be measured flow while the gas Gis brought into contact with the SUS316L-made substrate 2. Therefore,unlike the case with the conventional silicon-made substrate, there isno chance at all that the substrate 2 is corroded with the gas G.

FIG. 16 illustrate a mass flow rate sensor S according to the presentinvention being assembled into the main body part of the pressure typeflow rate control device. With FIG. 16, S designates a mass flow ratesensor, 31 a body, 32 a pressure detector, 33 a control valve, 34 apiezo-electric valve driving device, 35 an orifice, and 36 a filter.

FIG. 17 illustrates a mass flow rate sensor S according to the presentinvention wherewith the assembling position is altered. Therefore, FIG.17 is substantially identical to FIG. 16.

The constitutions of a pressure type flow rate control device and itsmain body part are publicly known, for instance, by U.S. Pat. No.3,291,161, the TOKU-KAI-HEI No. 11-345027 and the like. Therefore, theexplanation is omitted herewith.

EFFECTS OF THE INVENTION

According to the present invention, a substrate 2 to form the gascontacting parts of the resistance type mass flow rate sensor is madefrom a corrosion resistant material, and it is so constituted thattemperature detecting resistances 3 a, 3 b and a heater 4 are formed tobe thin-film-like by making use of micro-machine technologies.

Accordingly, the corrosion resistance of the gas contacting part isenhanced, and, at the same time, uniformity and compactness of theproduct characteristics, better response speed by decreasing the thermalcapacity, being particle-free and the like are all achieved. As statedabove, the present invention achieves excellent, practical effects whenin use not only with semiconductor manufacturing facilities but alsowith chemical plant-related facilities.

1. A corrosion resistant metal made thermal type mass flow rate sensorcomprising: (a) a sensor part comprising i. a corrosion resisting metalsubstrate having a fluid contacting surface, wherein the corrosionresisting metal substrate comprises an outer peripheral part and acentral part, wherein the central part comprises a thin plate that has athickness that is less than the thickness of the outer peripheral part;ii. a thin film forming a temperature sensor; and iii. a heater mountedon a rear face side of the fluid contacting surface of the corrosionresistant metal substrate; (b) a sensor base equipped with the sensorpart installed thereupon to secure hermeticity, and the corrosionresistant metal substrate is fastened hermetically to the sensor base,wherein the thin film comprises i. an insulation film formed on the rearface side of the fluid contacting surface of the corrosion resistantmetal substrate; ii. a metal film forming the temperature sensor on theinsulation film; iii. the heater formed on the insulation film; and iv.a protection film disposed to cover the insulation film and the metalfilm.
 2. A corrosion resistant metal made thermal type mass flow ratesensor as claimed in claim 1, further comprising: a fluid inlet forfluids flowing in; a fluid outlet for fluids flowing out; a body,wherein the sensor part fits into the body; and a metal gasket fastenedto the sensor base; wherein the body comprises a flow passage formedtherein for communicating between, and connecting, the fluid inlet andthe fluid outlet; and strain applied to the sensor part when fasteningthe metal gasket to the sensor base is suppressed by a stiffness ofmaterial of the sensor base against which the metal gasket fastens tosecure hermeticity between the sensor base and the body.
 3. A corrosionresistant metal made thermal type mass flow rate sensor as claimed inclaim 2, wherein the corrosion resistant metal substrate is formed withthickness of less than 150 μm.
 4. A fluid supply device comprising acorrosion resistant metal made thermal type mass flow rate sensor asclaimed in claim 2, wherein the corrosion resistant metal made thermaltype mass flow rate sensor is mounted on a fluid controller to checkflow rate appropriately at the time of fluid control.
 5. A corrosionresistant metal made thermal type mass flow rate sensor as claimed inclaim 1, wherein the corrosion resistant metal substrate is formed withthickness of less than 150 μm.
 6. A fluid supply device comprising acorrosion resistant metal made thermal type mass flow rate sensor asclaimed in claim 5, wherein the corrosion resistant metal made thermaltype mass flow rate sensor is mounted on a fluid controller to checkflow rate appropriately at the time of fluid control.
 7. A fluid supplydevice comprising a corrosion resistant metal made thermal type massflow rate sensor as claimed in claim 1, wherein the corrosion resistantmetal made thermal type mass flow rate sensor is mounted on a fluidcontroller to check flow rate appropriately at the time of fluidcontrol.
 8. A corrosion resistant metal made thermal type mass flow ratesensor as claimed in claim 1, wherein the insulation film is an oxidizedfilm with a thickness of 1.2 μm to 1.8 μm.
 9. A corrosion resistantmetal made thermal type mass flow rate sensor as claimed in claim 1,wherein the temperature sensor comprises a plurality of temperaturedetecting resistances formed by the metal film comprising a Cr/Pt/Crfilm.
 10. A corrosion resistant metal made thermal type mass flow ratesensor as claimed in claim 9, wherein the heater is formed by a metalfilm comprising a Cr/Pt/Cr film.
 11. A corrosion resistant metal madethermal type mass flow rate sensor as claimed in claim 1, wherein theprotection film is a SiO₂ film that is 0.4 μm to 0.7 μm thick.
 12. Acorrosion resistant metal made thermal type mass flow rate sensor asclaimed in claim 1, wherein the outer peripheral part of the sensor partis fixed into a flat fitting groove on a bottom surface of the sensorbase.
 13. A corrosion resistant metal made thermal type mass flow ratesensor comprising: (a) a sensor part comprising i. a corrosion resistingmetal substrate having a fluid contacting surface; ii. a thin filmforming a temperature sensor; and iii. a heater mounted on a rear faceside of the fluid contacting surface of the (b) corrosion resistantmetal substrate; (c) a fluid inlet for fluids flowing in; (d) a fluidoutlet for fluids flowing out; (e) a body, wherein the sensor part fitsinto the body; and (f) a metal gasket fastened to the sensor base;wherein the body comprises a flow passage formed therein forcommunicating between, and connecting, the fluid inlet and the fluidoutlet; and strain applied to the sensor part when fastening the metalgasket to the sensor base is suppressed by a stiffness of material ofthe sensor base against which the metal gasket fastens to securehermeticity between the sensor base and the body.
 14. A corrosionresistant metal made thermal type mass flow rate sensor as claimed inclaim 13, wherein the thin film comprises an insulation film formed onthe rear face side of the fluid contacting surface of the corrosionresistant metal substrate; a metal film forming the temperature sensoron the insulation film; a heater formed on the insulation film; and aprotection film disposed to cover the insulation film and the metalfilm.
 15. A fluid supply device comprising a corrosion resistant metalmade thermal type mass flow rate sensor as claimed in claim 14, whereinthe corrosion resistant metal made thermal type mass flow rate sensor ismounted on a fluid controller to check flow rate appropriately at thetime of fluid control.
 16. A fluid supply device comprising a corrosionresistant metal made thermal type mass flow rate sensor as claimed inclaim 13, wherein the corrosion resistant metal made thermal type massflow rate sensor is mounted on a fluid controller to check flow rateappropriately at the time of fluid control.